THE countdown has begun. Last week, US vice president Mike Pence announced that NASA is being directed to put astronauts on the moon by 2024 – the final year of president Donald Trump’s tenure, should he win re-election.

It is an ambitious goal and there are several obstacles to clear before we will see new bootprints in the lunar soil. Most crucially, reaching the moon requires a heavy-lift launch vehicle – a rocket that can boost 20 to 50 tonnes into low Earth orbit – to carry …